1. Field of the Invention
The present invention relates to a control system housing an electrical filter circuit to selectively filter out undesirable portions of a signal, such as noise, ripple, oscillations or vibrations occurring at frequencies within the bandwidth that the control system is expected to operate, while not affecting the large amplitude control signals present in the system.
Such a filter can be especially important in a control system such as used in a motorized wheelchair controller, wherein any tremor or spasticity occurring in an operator's hand or arm might cause erratic and potentially dangerous operation of the chair's drive motors. Controllers which respond to these tremor inputs may cause the chair to vibrate and move in undesirable ways.
2. Description of the Prior Art
Numerous attempts have been made to "soften" the operation of motorized wheelchair controllers in the past, including U.S. Pat. Nos. 4,415,049, issued Nov. 15, 1983, to John A. Wereb; 4,059,786, issued Nov. 22, 1977, to Michael Floyd Jones, et al.; and 3,814,199, issued Jun. 4, 1974, to William M. Jones. However, none has approached the problem in the same manner as the present invention. Prior attempts to filter or delay the undesirable low frequency tremor signals have compromised the response of the chair motors to inputs to the controller such that stopping or maneuvering the chair next to curbs, stairs, platforms, or vehicular or pedestrian traffic become unsafe.
In the art of electrical filters per se, adaptive filters such as those shown in U.S. Pat. Nos. 4,749,951, issued Jun. 7, 1988, to Yasushi Tanaka; 4,198,612, issued Apr. 15, 1980, to Roger R. A. Morton; and 3,889,108, issued Jun. 10, 1975, to Ben H. Cantrell represent attempts to filter an undesirable portion of the same signal, but none provides either the specific circuitry of the subject invention or the versatility of being able to cascade multiple stages of input filter circuitry to customize the control system for specific frequencies and/or amplitudes of the signals to be filtered as is possible with the present multi-window filter invention.
Other noise reducing systems and signal stripping circuits of the prior art have been noted, as shown by U.S. Pat. Nos. 4,322,641, issued Mar. 30, 1982, to Thomas N. Packard; 4,302,738, issued Nov. 24, 1981, to Richard C. Cabot et al.; and 3,889,136, issued Jun. 10, 1975, to William L. Mohan, et al., but none provides the flexibility and versatility of the present multi-window filter design in elimination of unwanted, low amplitude signal portions while passing the desired large amplitude control signals virtually unaffected.